Transcript Right Semi-Lunar Valve

Artificial Heart
Valves
Heart/Heart Valves
Heart consists of:
Right Atrium and Ventricle
Atrium
Left Atrium and Ventricle
Two Types of Valves:
Atrioventricular Valve:
separates the atrium from
the ventricle
Semi-Lunar Valve: separates
the ventricles from the
outgoing blood vessels
Heart/Heart Valves
Right Atrioventricular Valve:
Tricuspid Valve
Left Atrioventricular Valve:
Bicuspid Valve
Right Semi-Lunar Valve:
Pulmonary Valve
Left Semi-Lunar Valve:
Aortic Valve
Purpose of Valves: Prevent
backflow, or flow of blood
back into chamber from which
it came
Heart/Heart Valves
When Ventricle expands:
atrioventricular valve allows blood
to flow forward to the atrium into
the ventricle while the semilunar
valve prevents blood from flowing
back in heart
When Ventricle contracts:
atrioventricular valve closes to
prevent backflow while semilunar
valve allows blood to body or lungs
Prevention of backflow:
ensures the proper direction of flow
and reduces amount of work heart
must do to pump blood
When Heart Valves Stop Working
• Heart Valve diseases fall into two categories:
stenosis- hardening of the valve
incompetence- permittence of backflow
3 causes of Heart Disease:
Rheumatic Fever: stiffens valve tissue, causing stenosis
Congenitally defective valves: do not form properly as
the heart develops, but often go unnoticed until
childhood
Bacterial infection: causes inflammation of valves, tissue
scarring, and permanent degradation
History
1952- The first ever invented artificial heart valve was designed
by Charles A. Hufnagel which was the caged-ball design
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1955- Judson Chesterman implanted the first successful heart
valve (at the City General Hospital in Sheffield, England)
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The patient lived 14 hours after the valve was placed, but died
when the poppet twisted out of position
1960- the first human was implanted with the ball and cage
design
Binet and associates, started using porcine aortic valves for
humans
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1969- The Bjork-Shiley valves was the first tilting-disc design to
come out
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1979-the bileaflet design was introduced which was composed
of two semicircular leaflets that shifted open and closed
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Types of Artificial Heart Valves
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MechanicalThere are three types. The caged ball, tilting disk,
and bileaflet
Tissue(biological)Valves that are used from animals to implant them
back into humans
Evolution of Prosthetic Heart Valves
This first heart valve was made
of a Plexiglass(methyl
methacylate) cage
surrounding a silicone-coated
nylon poppet
First implanted in a human in a
closed procedure in
September of 1952
(descending thoracic aorta)
Evolution of the Prosthetic Heart Valve
• Starr-Edwards valve was first
successful long-term valve
created
• It was implanted in its first 8
patients in 1961 (6 of 8 survived
• Ball-and-Cage design
• Devised important “Nine
Commandments” in developing a
prosthetic heart valve
Evolution of the Prosthetic Heart Valve
• Since this time, over 30
mechanical heart designs have
been marketed in the U.S. and
abroad
• These valves have progressed
from the simple caged ball
valves, to strut-and-leaflet
valves and the modern bileaflet
valves, to human and animal
tissue
Evolution of Prosthetic Heart Valves
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“Nine Commandments”:
Embolism Prevention
Durability
Ease and Security of Attachment
Preservation of Surrounding Tissue Function
Reduction of Turbulance
Reduction of Blood Trauma
Reduction of Noise
Use of Materials Compatible with Blood
Development of Methods of Storage and Sterilization
Mechanical Heart Valves
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All the types of mechanical heart valves are still in use today.
Usually made of titanium or carbon which makes them strong and
very durable
Three types of mechanical heart valves
Tissue Heart Valves (biological valves)
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Using valves from other animals. The
procine valve of a pig is the most
comparable valve to a human.
Xenotransplantation
Pericardial valves: Biological valve tissue
can be taken from a cow or horses
pericardial sac and be sewed to a metal
frame.
Advantages
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Mechanical heart valves:
The biggest advantage is the durability. While the tissue heart
valves are estimated to last about 10-15 years, a mechanical heart
valve can last 30 year.
Tissue heart valves:
There is minimal blood regurgitation, minimal transvalvular pressure
gradient, self repairing.
Does not require and anti-coagulant drug.
Advantages & Disadvantages
Mechanical heart valves
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In order to decrease the risk of blood clotting,
the patient must take blood thinners, Have
serious problem with thromboembolism, fail
suddenly and catastrophically
Some patients can hear their mechanical
heart valve open and close.
Tissue heart valves
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Patients do not need lifelong anticoagulant
therapy
Inexpensive and mass-produced
Wear, there is a small possibility that the body
will reject the valve, inability to implant
them into infants and children.
uncertain durability (5-15 years) that will
inevitably require a risky re-operation
Artificial Heart Valve Types
Figure. Algorithm for selecting a valve procedure.
El Oakley R et al. Circulation 2008;117:253-256
Copyright © American Heart Association
Mechanical Valves:
Ball Valves
• This design uses a spherical occluder, or blocking
device, held in place by a welded metal cage
Problem and Why failed:
Natural heart valves allow blood to flow straight
through the center of the valve (central flow)
Caged-ball valves completely blocked central flow and
collisions with the occluder ball caused damage to
blood cells
Finally, these valves stimulated thrombosis, or formation
of blood clots
Starr-Edwards Ball Valve
Model: Starr-Edwards
Type: Aortic Caged Ball
Materials:
Silicone Rubber ball with 2%
barium sulfate
cage: Stellite alloy No. 21,
sewing ring- knitted Teflon
and polypropelene cloth
1 of 4 Starr-Edwards models
developed are still used
today, and is the only ball
valve currently used in U.S.
Magovern-Cromie Ball Valve
Model: Magovern-Cromie valve
Type: Aortic Caged Ball
Materials:
Ball: Silicone rubber with barium,
cage: Titanium,
sewing ring-none,
Cage open at top
Smeloff-Suttor Ball Valve
Model: Smeloff-Suttor valve
Type: Aortic, Mitral, Tricuspid
caged ball
Materials:
Ball: Silicone rubber,
cage: Titanium,
sewing ring:Teflon
Problems:
Ball Variance, swelling of ball from
lipid absorbtion, can cause
sticking of ball in inflow orifice
Mechanical Valves:
Single Leaflet Disc Valves
• Uses a tilting occluder disk
to better mimic natural flow
patterns through the heart
• tilting pattern allow more
central flow while still
preventing backflow
• Some damage still occurs to
blood cells
• Reduces thrombosis and
infection, but does not
eliminate either problem
Bjork-Shiley Standard Aortic Valve
Model: Bjork-Shiley
Standard
Type: Aortic Tilting Disc
Materials:
Disk: Pyrolytic Carbon,
cage: Haynes 25, sewing
ring:Teflon
Bjork-Shiley Prosthetic Heart Valve
• In 1979, the Bjork-Shiley valve
was modified to open from 60 to
70 degrees (Convexo-Concave
valve)
• 82,000 were implanted between
the time of its invention and its
removal from the market in 1986
• Between 1979 and 1990, 600
fractures occurred with 2 out of
3 fractures resulting in death
Impact of Bjork-Shiley ConvexoConcavo(BSCC) Heart Valves
• In 1979, the Bjork-Shiley valve was approved very quickly, only
six months after Shiley’s first request
• The main criticism of the FDA was its delay in removing the
valve from the market despite knowledge of the outlet struts
susceptibility to fracture
• The Bjork-Shiley heart valve failure prompted the FDA to
make substantial changes in its policies
• The deaths and sicknesses have greatly effected Shiley
Incorporated, the FDA, and the medical industry
• Overall, Shiley and its associate company, Pfizer, have faced
hundreds of lawsuits and paid more in legal fees and lobbying
costs than if they had simply replaced the valves
• According to the Federal Device Amendments, the BSCC is a
justified killer
Medtronic-Hall Valve
Model: Medtronic-Hall
A7700 (aortic), M7700
(mitral)
Type: Aortic and Mitral
Tilting Disk
Materials:
Cage: Titanium,
Disk: Pyrolytic carbon,
sewing ring: knitted teflon
Other Single Leaflet Disc Valves
• Another similar valve is the
caged disc valve
• Examples are Starr-Edward
Model 6500 and the KayShiley Model
Mechanical Valves:
Bileaflet Disc Heart Valves
• Consists of two semicircular
leaflets that pivot on hinges
integrated onto the flange
• Carbon leaflets and flange
exhibit high strength and
excellent biocompatibility
• Provide closest approximation
to central flow
• Allows small amount of
backflow as leaflets cannot
close completely
St. Jude Bileaflet Valve
Model: St. Jude Valve
Standard
Design :Mitral, Aortic,
Tricuspid Bileaflet Valve
Materials:
Cage and disk: Pyrolytic
carbon,
sewing ring: Double velour
knitted polyester
Animal Tissue Valves
• Heterograft or Xenograft
Vavles
• Most commonly used tissues are
the porcine (pig) valve tissue
and Bovine (cow) pericardial
tissue
Porcine (pig) Valves
• Two major brands of porcine
available today, Hancock and
Carpentier-Edwards
• Has good durability and good
hemodynamics
Materials:
Porcine valve tissue,
stents made of wire,
Elgiloy (cobalt-nickel alloy),
sewing ring: knitted Teflon
Pericardial (cow) Valves
• Lasts as long as standard porcine
valves at 10 years
• The pericardial valve has
excellent hemodynamics, even
in smaller sizes (19 - 21mm) and
has gained a large market share
(about 40% of US tissue valves)
in this group of patients
Stentless Porcine Valve
Homografts (Human to Human)
• Homografts are valves transplanted from
one human to another
• After donation, valves are preserved in liquid
nitrogen (cyropreserved) until needed
• Since the valve must be thawed overnight,
the patient’s size must be known beforehand
• As with heart transplants, homograft
availability is limited by donor availability
Autografts (Ross Procedure)
• Autografts are valves taken from the same patient in
which the valve is implanted
• Used for patients with diseased aortic valves
• Advantages: patient receives a living valve in the
aortic position
Better durability and hemodynamics
Disadvantages: difficult procedure for the surgeon
and involves considerable skill and time
most common problem is leakage of the valve (aortic
regurgitation)
Implanting
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Both mechanical and tissue heart valves require open
heart surgery
It’s more common in tissue valves for a re-operation
Complete recovery from surgery could be a couple of
weeks to several months
Currently: 55% mechanical valves
45% tissue valves
Future of heart valve replacement
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Polymeric Heart Valves - Scientists are looking more
into polymer materials for heart valves because it’s
easy to fabricate, has a large range of polymer
properties, and durability.
Tissue engineered heart valves- Obtaining the number
of types of cells for tissue valves, lack of scaffold
material